Method for the removal of unwanted portions of an article

ABSTRACT

A method for the removal of unwanted portions of an article such as burrs and flashing utilizing solid particles of ice which are impacted against the unwanted portions is described. The ice particles are maintained in a flowable condition prior to impact by a cooling agent. The cooling agent is in a heat transfer relationship with the ice particles, usually in direct contact with them. Examples of cooling agents which can be mixed with the ice particles and which are easily removed with them are, for instance, solids such as solid carbon dioxide, liquids such as liquid nitrogen or cooled alkanols and/or lower alkanols containing water and cooled gases such as air, carbon dioxide or nitrogen. Kinetic energy imparted to the ice particles causes removal of the unwanted portions of the article upon impact. In addition, the ice particles, and cooling agent when used, cools the impacted area and with thermoplastic and elastic materials thereby embrittles thin sections of flashing and burrs and the like making them more easily removable by the impact of the ice particles.

O United States Patent 1151 3,676,963

Rice et al. 1451 July 18, 1972 54] METHOD FOR THE REMOVAL OF 3,137,101 6/1964 Leliaert ..51/13 UNWANTED PORTIONS OF AN 3,160,993 12/1964 McCormick ARTICLE 3,324,605 6/1967 Lester ..51/314 [72] Inventors: Edwin Eugene Rice; Charles Henry Primary Examiner-Lester M. Swingle Franklin, both of Ann Arbor, Mi h, Attorney-Miller, Morriss, Pappas & McLeod [73] Assignee: Chemotronlcs International, Inc., Ann Ar- [57] ABSTRACT bor, Mich. A method for the removal of unwanted portions of an article [22] F'led: March 1971 such as burrs and flashing utilizing solid particles of ice which [21] AppL No; 122 152 are impacted against the unwanted portions is described. The ice particles are maintained in a flowable condition prior to impact by a cooling agent. The cooling agent is in a heat [52] U.S.Cl.... .....5l/320,51/ 164.5, 241/184 transfer relationship with the ice particles, usually in direct [51] Int. Cl. ..B24c l/00 contact with them. Examples of cooling agents which can be [58] Field of Search ..51/320, 313, 314, 315, 316, mixed with the ice particles and which are easily removed with 51/1645, 8, 13; 241/184; 83/22, 177; 225/1 them are, for instance, solids such as solid carbon dioxide, liquids such as liquid nitrogen or cooled alkanols and/or lower 56] References Ci d alkanols containing water and cooled gases such as air, carbon dioxide or nitrogen. Kinetic energy imparted to the ice parti- UNITED STATES PATENTS cles causes removal of the unwanted portions of the article upon impact. In addition, the ice particles, and cooling agent 2 gopphn 3 when used, cools the impacted area and with thermoplastic 2682732 4 l l and elastic materials thereby embrittles thin sections of flash- 7/195 Hamahan et "51/13 X ing and burrs and the like making them more easily removable 2,881,571 4/1959 Granata et al. ..51/314 X by the impact ofthe ice particles 2,996,846 8/1961 Lehaert ..51/13 3,110,983 11/1963 Moore ..51/314 X 10 Claims,2Drawing Figures PROVIDING ICE PARTICLES WITH COOLING AGENT WHICH STEP I IS A VAPOR AT ELEVATED TEMPERATURES USED FOR DRYING.

IMPACTING ICE PARTICLES ON UNWANTED THIN PORTIONS L 2 OF ARTICLE.

REMOVING ANY REMAINING WATER, ICE OR COOLING STEP 3 AGENT BY DRYING.

rmmenmemz FIG! PROVIDING ICE PARTICLES WITH COOLING AGENT WHICH IS A VAPOR AT ELEVATED TEMPERATURES USED FOR DRYING.

IMPACTING ICE PARTICLES ON UNWANTED THIN PORTIONS OF ARTICLE.

REMOVING ANY REMAINING WATER, ICE OR COOLING AGENT BY DRYING- FIG. 2

STEP l STEP 2 METHOD FOR THE REMOVAL OF UNWANTED PORTIONS OF AN ARTICLE PRIOR ART in general the prior an describes various methods of and equipment for the removal of unwanted portions of an article involving the use of conventional solid particles, such as finely divided sand, steel, glass and the like, which require subsequent removal, usually by washing, from internal portions of the treated article. Examples of such methods are those described in US. Pat. Nos. 2,996,846 (Re. 25,554), 3,1 10,983; 3,137,101 and 3,160,993.

In many instances pockets, holes and the like in the article being treated accumulate or trap conventional solid particles making their removal difficult and expensive. This is particularly a problem where the articles being treated have blind or narrow internal passages or pockets.

Present methods using such prior art particles are satisfactory for removing flashing and the like from thermoset plastics since such flashing is quite rigid and breaks upon impact with the particles. However, flashing and the like on thermoplastic and/or elastic materials tends to deform rather than to break and thus is not so easily removed.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method wherein the impacting material is easily removed from the treated article, particularly from internal passages inside an article being treated and can be removed without specific direct treatment by the user simply by allowing drying under ambient room temperature conditions. It is further an object to provide a method wherein flashing, burrs and the like are easily removed from thermoplastic and/or elastic materials.

These and other objects will become increasingly apparent from the following description and the drawing:

FIG. 1 is a schematic diagram of the steps in the method of the present invention.

FIG. 2 schematically illustrates the preferred spray imparting of ice on the surface of an article.

The objects of the present invention are accomplished by the method for the removal of unwanted portions of an article which comprises: providing solid ice particles in a heat transfer relationship with a cooling agent which maintains the particles in a flowable condition; impacting the unwanted portions with the flowable ice particles so as to remove the unwanted portions; and removing any remaining ice particles, water or cooling agent from the article using drying conditions. As a result of storing, handling or processing the treated article at room temperature, the ice particles will melt and eventually evaporate and the selected cooling agent if it remains on the surface at all is vaporizable with the water from the ice particles upon warming so that there is no residue remaining on the surface.

The ice must be solid and hard in order to be effective for the removal of unwanted portions of an article. This means that the ice usually has a density between about 0.89 and 0.98 g/cm (See Science, Vol. 171, Jan. 8, 1971 at page 63) and is substantially non-porous although it may have occluded gas bubbles retained upon freezing of the water. The particles are readily formed using conventional crushing techniques-from larger blocks of ice and then screening the resulting ice particles for size. Alternatively the particles can be formed by freezing droplets of water in a cooling agent gas or liquid stream.

Once formed, the ice particles must be maintained in a flowable condition by cooling them substantially below freezing. This is accomplished by using the cooling agent to maintain the ice particles at a temperature of less than about 25 F. This prevents the surfaces of the ice particles from melting under packing pressures and bonding together due to a snow balling" efiect. Preferably the particles are cooled to temperatures of less than about F to 300 F. The lowering of the temperature of the ice particles in this manner also has the effeet of hardening them so that they can remove unwanted portions of articles that would normally be considered to be resistant to such removal.

The cooling agent functions to transfer heat from the ice particles before use. In most instances, the cooling agent is in direct contact with the ice; however, it will be appreciated that a heat exchanger can be used to cool the ice particles in absence of direct contact with the cooling agent. Also, even if the cooling agent is in contact with the ice where airless impacting techniques are used, the cooling agent need not be subsequently impacted on the article along with the ice particles. Such variations will be obvious to those skilled in the art.

In general, the cooling agent can have any desired composition and can be liquid, gaseous or solid so long as if it remains on the treated article it is a vapor at elevated temperatures used to dry the article to remove water and which must be below the destruction point of the article and so long as it is not a solvent for, or a reactant with, the article being treated. Examples of cooling agents which can satisfactorily be mixed with the ice particles and which can be removed under water drying conditions are gases, such as air, liquids such as liquid nitrogen, water containing lower alkanols or other water miscible freezing point depressing chemicals (tetrahydrofuran) in combination with water and solids such as solid carbon dioxide. Elevated or reduced pressures can be used to regulate the physical state of the cooling agent with the ice particles; however, ambient pressures are preferred for reasons of economy. Preferably the cooling agent is a vapor at ambient room temperatures and thus is removed by normal warming of the article.

As a matter of economics, when the ice particles are mixed with the cooling agent it is best to use the largest amount of ice and the smallest amount of cooling agent which maintains the ice in a flowable condition before impact on the unwanted portions of an article and which allows the ice to accomplish removal of such portions. For instance, the ratio for a mixture of solid carbon dioxide and ice particles is preferably at least about 0.5 to 1.

Various means can be used to impact the ice particles on the unwanted portions of an article. For instance, a gas stream can be driven through a conventional aspirator nozzle such that ice particles are aspirated into the gas stream through a conduit leading into the stream using a vaccum effect. The ice particles can be driven directly through a nozzle in a gas stream. The ice particles can be used in a tumbler. Gas blowers or airless mechanical impellers for the ice particles can be used. All of these expedients are well known to those skilled in the art. The selection is easily made depending upon the kinetic energy required to remove unwanted portions from a particular article with ice particles due to its construction or composition.

The ice particles (as well as the cooling agent if it is also impacted on the surface) additionally function to embrittle thin portions present as part of the impacted portions of the article. This embrittlement greatly aids in the removal of the thin portions upon subsequent impact by ice particles and is particularly useful with thermoplastic or elastomeric articles due to the rigidifying of thin sections whose flexibility makes their removal difficult at ambient temperatures. In addition, energy is conserved as only treated areas are subjected to cooling. In this way delicate articles that might be damaged by complete cooling would have only the treated area differentially cooled. This result is particularly evident with flashing or burrs on flexible, elastic or thermoplastic polymers both natural and synthetic wherein such embrittlement aids the removal of the flashing or burrs.

Plastics, metals, ceramics and the like can be treated by the method of the present invention providing the hard ice particles are impacted against the unwanted portions of articles composed of such materials with sufficient energy. The treatment of the relatively softer or more flexible articles is particularly preferred since the action of the hardened ice is most effective against unwanted portions of these articles. Of course,

it is not usually desirable to treat materials which are damaged when any residual ice particles melt, such as by dissolving or reacting with the material being treated.

Articles having all sorts of shapes due to fabricating steps can be treated by the method of the present invention and such fabrication includes machining, stamping, molding and the like. The spraying method of the present invention is particularly useful for instance as an improved method for the reticulation (cell membrane removal) of sheets of foam materials such as cellular polyester or polyether polyurethanes to make the cells more open and interconnected. In this instance, the easy removal of the impacting agent is particularly necessary and would be extremely difficult if conventional non-volatile particles were used because of the large number and small diameters of the cells and their consequent filtering and entrapment action.

The ice particles are easily and economically removed. A blast of cooled gas can be used before the ice particles melt substantially. In some instances it may be desirable to use a heated gas stream for forced drying or altematively to allow the article to dry by warming to ambient conditions with draining and evaporation of the water forming the ice particles. Various drying methods for removing the ice particles and/or water are well known to those skilled in the art.

The present invention also includes the use of dissolved or dispersed chemicals in the water forming the ice for various known purposes, such as the use of chemicals for inhibiting the formation of rust in ferrous materials by the water from the melted ice. Also, various chemicals which increase the sharpness or abrasiveness of the ice crystals by promoting sharp cleavage in forming the particles or tempering them can be used.

The ice particles and any cooling agent particles can be of any desired size depending upon the application. For instance, it is preferred for reticulating foam that the particles have a diameter between about one two-hundredth inch and one-sixteenth inch. This allows the particles to easily penetrate the small internal passages of the above discussed foams. Thus where articles have internal passages requiring treatment, the particles should easily enter such passages. Conversely, if treatment is to be avoided, the particles should be larger than the passages or impact otherwise restricted. Also, large pellets or particles of ice can be used which shatter on impact with a surface.

SPECIFIC DESCRIPTION The following are non-limiting specific examples of the method of the present invention.

EXAMPLE I Referring to FIGS. 1 and 2, ice particles were reduced to a particle size of about 20 mesh and then cooled to about minus 50 F in a carbon dioxide atmosphere. An aspirator nozzle 11 with about a 0.2 inch diameter venturi throat l2 and a 0.3 inch diameter discharge opening 13 with a small orifice 14 (0.1 inch in diameter) concentric with the venturi throat 12 just past the inlet conduit 15 for the ice particles 10 was used with the ice. The section of the nozzle 11 downstream from the ice inlet was about 4 inches long. Air from a compressor 16 was driven through the orifice 14 in the nozzle 11 which then aspirated the ice particles 10 from a container 19 and then the air and ice 10 passed through the venturi throat 12 and out the nozzle 11. The air was precooled to about minus 10' F to minimize any warming of the cooled ice particles 10. The air pressure upstream of the orifice 14 from the supply was about 100 pounds per square inch guage.

A clear methyl methacrylate (Plexiglass block 17 was cut with a hand saw so that cutting burrs 18 remained. The block 17 was then impacted with the ice particle to spray from the noule 11. It was found that the sawing burrs 18 were effectively removed. An equivalent result was achieved by impacting a steel article with burrs made by an end milling operation and a zinc diecast part with flashing. The surface of a sheet of polyester polyurethane foam (about 10 pores per linear inch, about 1.8 pounds per cubic foot and one-quarter inch thick) was sprayed to remove the membranes from the cells. The sheet was completely reticulated and the remaining cell struts were firm and intact. In all instances, the entrapped or residual ice was easily removed upon warming to ambient temperatures.

EXAMPLE II A mixture of ice and dry ice particles (carbon dioxide in solid form) both about 16 mesh in about a l to l by volume mixture was driven through the aspirator nozzle of Example I by air at a temperature of about minus 10 F. Various materials were impacted with the spray to remove burrs or flashing from fabricating. Buns were removed on parts made of polyacetal (DELRIN M polytetrafluoroethylene (TEFLON polyurethane, polypropylene, polyester molded with sisal and plasticized polyvinyl chloride. Mechanically shaped steel, cast iron and zinc diecast parts were effectively deburred in the same manner. Rust was also removed from the steel part. The dry ice sublimed from the surface upon being exposed to ambient conditions and the ice melted and evaporated upon warming.

EXAMPLE III The procedure of Example II was repeated except that the air from the compressor was not cooled. It was found that the presence of the dry ice was sufficient to maintain the temperature of the ice so that it was flowable and the results were essentially as good.

EXAMPLE IV Ethanol as the cooling agent was cooled to about minus 20 F and added to crushed ice with a particle size of about 0.05 inch in a ratio of l to l by volume to form a slush. The mixture was sprayed in the apparatus of Example I and a zinc diecast part was deburred. Various plastic parts were also deburred, the only limitation being that the ethanol does not significantly dissolve the plastic. This ice-ethanol mixture was also pressurized directly out of a nozzle rather than aspirated. This was accomplished by using high pressure bottled nitrogen to pressurize the mixture to about 800 psi and it satisfactorily deburred the treated articles. Water was also used with the ethanol-ice mixture in amounts such that the resulting solution did not freeze. Drying was accomplished by warming to ambient temperatures.

EXAMPLE V An acrylic plastic part one-quarter inch thick and 1 inch square with a 16 inch diameter hole was tumbled in a mixture of coarse ice particles mixed with particles of solid carbon dioxide (which acted as a cooling agent for the ice particles of 0.5 inch approximate maximum dimension) for about 30 minutes. The hole had a large drill exit burr covering about one-quarter of the hole. It was found that the burr was removed and that the surface was smoothed by abrasion. Any remaining water was removed by drying.

Liquid cooling agents such as liquid nitrogen can be ejected in a spray or cutting jet with the ice particles using known methods. Illustrative is the following example wherein boiling liquid nitrogen (-1 C at one atmosphere is used to propel the ice particles.

EXAMPLE VI A second aspirator nozzle similar to that of Example I was used with no venturi throat and with a k inch diameter nozzle and a 0.15 inch orifice about 1 inch upstream from a 1% inch inlet opening for the ice at a right angle to the nozzle. The nozzle was 8 inches long past the ice inlet opening. Ice particles no larger than three-sixteenths inch in diameter were aspirated from the container, with boiling liquid nitrogen (about minus 295 F) driven through the orifice and nozzle at near sonic velocities. Mold flash on hot formed glass filled polypropylene sheet was completely removed without damage to the remainder of the article. Any remaining water was removed by drying.

It will be appreciated that various airless" techniques can also be utilized as are known in the prior art wherein the ice particles derive momentum by means other than from a gas stream as for example by centrifugal force.

EXAMPLE VII To illustrate the airless technique a blower with radially extending vanes 4 inches long and 1% inch wide rotating on a shaft in a housing was used. An inlet reservoir funnel attached to the blower housing for an ice-solid carbon dioxide mixture of pellets (large particles) about one-half inch in diameter fed the pellets to the rotating vanes, which shattered them into smaller ice particles and exited them through a tangential outlet. Cast aluminum which had been milled leaving burrs was effectively deburred. Any remaining water was removed by drying.

The following example shows the use of a mixture of ice and a lower alkanol as the cooling agent.

EXAMPLE Vlll A mixture of equal parts by volume of ice particles and methyl alcohol mixed in equal parts by volume with water and which had been pre-cooled to well below 32 F was prepared as a slush. The mixture was loaded into a cylindrical gun about 20 inches long and with a 2% inch diameter. A 3/16 inch diameter bore discharge nozzle was located at one end of the gun. A filler plug was provided at the breech of the gun and the gun was connected through the filler plug to a high pressure nitrogen tank (1,500 psi). The gun was charged with the ice particles, water and methanol mixture and the nitrogen source triggered so that the gun discharged about perpendicularly to a projection of flashing on a zinc diecast part. It was found that the flashing was completely removed from the part by the ice particles. Any remaining water was removed by drying.

It will be appreciated that the ice particles can also be formed by introducing a spray of water into a stream of a gaseous or liquid material which is at a temperature less than about 25 F. Such gaseous materials are for instance: carbon dioxide, nitrogen or organic compounds having a low boiling point (fluorocarbons). All of such variations of forming the ice particles will be obvious to those skilled in the art.

We claim:

1. The method for the removal of unwanted thin portions of an article which comprises:

a. providing solid ice particles consisting essentially of water in a heat transfer relationship with a cooling agent which maintains the temperature of the particles at less than about 25 F so that they are in a hardened and flowable condition and which is a vapor at the elevated temperatures used in drying to remove water from the surfaces of an article;

b. impacting the unwanted portions of the article with ice particles in said flowable and hardened condition by moving said ice particles in a gas stream so that said ice particles have sufficient kinetic energy to remove the unwanted thin portions; and

c. removing any remaining ice particles, water or cooling agent from surfaces of the article using drying conditions.

2. The method of claim 1 wherein the cooling agent is solid carbon dioxide.

3. The method of claim 1 wherein the cooling agent is liquid nitrogen.

4. The method of claim 1 wherein the cooling agent is a gaseous material at a temperature below about 0 F.

5. The method of claim 1 wherein the ice particles are impacted on the unwantedportions as a s ray.

6. The method of claim 1 wherein t e ice particles are impacted in the form of a cutting jet.

7. The method of claim 1 wherein the ice and a cooling agent selected from solids and liquids are in admixture which are impacted on the article and are removed by contact with a warmer atmosphere.

8. The method of claim 1 wherein the particles are formed by injecting water into a stream of the cooling agent so as to freeze the water into particles of ice.

9. The method of claim 1 wherein the article is a flexible thermoplastic with projections selected from waste flashing and burrs which are rigidified upon being cooled by the impacting ice particles and removed by the impact of the ice particles.

10. The method of claim 1 wherein the solid ice particles have a density between about 0.89 to 0.98 g/cm. 

1. The method for the removal of unwanted thin portions of an article which comprises: a. providing solid ice particles consisting essentially of water in a heat transfer relationship with a cooling agent which maintains the temperature of the particles at less than about 25* F so that they are in a hardened and flowable condition and which is a vapor at the elevated temperatures used in drying to remove water from the surfaces of an article; b. impacting the unwanted portions of the article with ice particles in said flowable and hardened condition by moving said ice particles in a gas stream so that said ice particles have sufficient kinetic energy to remove the unwanted thin portions; and c. removing any remaining ice particles, water or cooling agent from surfaces of the article using drying conditions.
 2. The method of claim 1 wherein the cooling agent is solid carbon dioxide.
 3. The method of claim 1 wherein the cooling agent is liquid nitrogen.
 4. The method of claim 1 wherein the cooling agent is a gaseous material at a temperature below about 0* F.
 5. The method of claim 1 wherein the ice particles are impacted on the unwanted portions as a spray.
 6. The method of claim 1 wherein the ice particles are impacted in the form of a cutting jet.
 7. The method of claim 1 wherein the ice and a cooling agent selected from solids and liquids are in admixture which are impacted on the article and are removed by contact with a warmer atmosphere.
 8. The method of claim 1 wherein the particles are formed by injecting water into a stream of the cooling agent so as to freeze the water into particles of ice.
 9. The method of claim 1 wherein the article is a flexible thermoplastic with projections selected from waste flashing and burrs which are rigidified upon being cooled by the impacting ice particles and removed by the impact of the ice particles.
 10. The method of claim 1 wherein the solid ice particles have a density between about 0.89 to 0.98 g/cm3. 